Life on the mudflats

In the mudflats, the treasure is buried

The mudflats are full of both algae and benthic animals. And while it may not be a treasure trove of gold, it is a veritable treasure trove of food for birds and fish. Compared to the average seabed, the mudflat contains ten times more animals by weight. With a total area of 4,700 square kilometres, this makes the mudflats a gigantic pantry. The conditions for the rich wildlife are created in particular by the tides, which bring nutrient-rich water into the shallow Wadden Sea twice a day. The basis for life is the high abundance of microscopic algae, especially diatoms, which form the first link in the food chain. Diatoms live floating in the water, on the surface of the mudflats and down in the mudflats. It is also the diatoms that give the mudflats their brown colour. In just 1 cm2, there can be up to 2.5 million diatoms, which are the primary food source for benthic animals such as sandworms, snails and small crustaceans. The bottom dwellers in turn become food for birds and other larger animals.

The right mix

The rich life in the mudflats is dependent on the right mix of sand and clay - the so-called candy. The largest number of animals live in places where the mud makes up up to a fifth of the bottom. If the bottom is pure sand or pure mud, there are only a few animals. Most of the animals in the wadden are quite small, but they often appear in staggering numbers. There can be over 100 roundworms in just one cubic centimetre of mudflat. Living on top of the wadding is the dune snail, which measures just a few millimetres and is therefore easily overlooked. But they are extremely numerous: in just one square metre, there can be up to 120,000 snails.

Experience the wadden sea

There are great opportunities to get up close and personal with the life of the wadden. And there is something for every taste and temperament. If you are up for it, you can easily explore on your own. If you want to dig up mussels, it is a good idea to bring a grab - it makes it a little easier. You can also take the kids with you and let them walk around the mudflats in bare feet, so they can really feel the lick between their toes. It is exciting to explore the hidden life of the mudflat, but as it is not safe to go far out on the mudflat, it is a good idea to be well prepared to avoid unpleasant surprises. It is therefore advisable to plan your trip based on the tide forecast and decide in advance when you will return. You can also book a guided tour with one of our partners - a knowledgeable guide will take you out on the water and make sure you have a great experience.

The characteristic small piles of sand bear witness to the sand worm's activity below the surface

Read more about the microscopic wildlife of the mudflats

One of the most abundant animals in the mudflats is the small lick crab, which in some places can be found in quantities of up to 100,000 individuals per square metre. The lick crab lives in tunnels in the seabed and feeds on decomposed plant material and bacteria that it filters from the water or collects from the seabed. The burrowing activity of the lick crab is important for the chemical metabolism of the mud and for the stability of the seabed.

The sand worm is hugely important to the mudflat. The worm grows 15-20 cm long and lives down in the mudflats in a U-shaped tube. Here it feeds on sand and utilises the microscopic algae on the surface of the sand grains. The worm deposits its faeces by sticking the end out of its protective tube - evidence of its activity can be found all over the mudflats in the form of the characteristic small piles of sand. The sand worm is so important because its tube carries water down into the sand, allowing many other organisms to live deep in the seabed. The sand worm is also an important part of the fish's diet.

The horse shrimp is very common and can be found almost everywhere in Danish waters. It typically lives on sandy bottoms in shallow water. This makes the Wadden Sea a particularly good place for horseshoe crabs, and there are large numbers here - up to 100 horseshoe crabs per m2 have been counted. The horseshoe crab can grow up to 8 cm long and belongs to the group of crustaceans known as the "10-legged crustaceans". Many fish eat the horse prawn, and it is also sought after by humans. In some restaurants in the Wadden Sea region, it is served as Wadden Sea prawns.

The cockle lives almost its entire life buried 1-2 cm in the sandy mudflats. Here it feeds primarily on algae via its two breathing tubes. One tube is an intake tube where water is sucked in and filtered for algae inside the mussel's gills. The filtered water is excreted through the other breathing tube. Inside its shell, the mussel is a mollusk that is a favourite food for many birds - especially the oystercatcher, which can smash the shell or wedge it open with its beak. Inside the shell, the cockle has a powerful foot that it can push out between the shells and use to dig down. If you dig up a live cockle and place it in the water, it will quickly bury itself again.

Boy fishing for horse prawns. In some restaurants in the area, it is served as mudflat prawns

How to be the best guest when exploring the mudflats

We prepare at home and have checked the tide table at DMI (https://www.dmi.dk/hav-og-is/temaforside-tidevand/tidevandstabeller/) so that we don't get caught in high tide while on the wadden sea
We never go out in fog and always bring a compass and mobile phone so we can find our way in case of sudden sea spray or fog.
We remember that we are guests in nature and avoid disturbing birds, seals and other animals.
We pick up any rubbish we find and take it with us - even if it's not our own.

Fotos: Petra Grundmann, Lars Maltha Rasmussen

Life on the mudflats

In the mudflats, the treasure is buried

The right mix

Experience the wadden sea

Read more about the microscopic wildlife of the mudflats

How to be the best guest when exploring the mudflats

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